Hold-down anchor device for the embedded cables of prestressed concrete girders



HILLBERG 3,006,114 HOLD-DOWN ANCHOR DEVICE FOR THE EMBEDDED CABLES OF PREsTREssED CONCRETE GIRDERS Filed Aug. 10, 1959 Oct. 31, 1961 2 Sheets-Sheet J.

INVENTOR: BROR HILLBERG ATT'YS Oct' 31, 1961 B. HILLBERG 4 HOLD-DOWN ANCHOR DEVICE FOR THE EMBEDDED CABLES 0F PRESTRESSED CONCRETE GIRDERS Filed Aug. 10, 1959 2 Sheets-Sheet 2 INVENTOR: BROR HILLBERG ATT'YS 6 Claims. (Cl. 50-430) The present invention relates to structural forms and more particularly to a novel form of hold-down anchor device by means of which the tensioning cables which are embedded in a prestressed concrete girder may be held taut under tension and in their proper relative positions within the girder form during initial pouring and subsequent hardening or setting of the cement so that when the tension in the cables is relieved after the concrete has become set and the projecting or overlapping ends of the cable severed from the ends of the girder, the material of the girder will remain prestressed, thus providing a girder which possesses greater strength than conventional girders which are not prestressed in this manner. Girders of the type with which the present hold-down anchor device is associated are of the portable type, which is to say that they may be preformed as 'a composite unit and thereafter transported bodily to a scene of installation. Such girders may assume various cross sectional shapes and, for exemplary purposes herein, the hold-down anchor device has been illustarted in connection with the construction of a girder which is generally of I-shape in cross section and which will, for convenience, hereafter be referred to as an I-beam. It will be understood, however, that the present hold-down anchor device may be found useful in the formation of prestressed concrete girders having a wide variety of shapes.

In the construction of prestressed concrete girders of the type briefly outlined above, the tensioning cables, of which there may be a relatively large number, are ordinarily strung" longitudinally through the hollow girder form in different but generally longitudinally extending directions. Certain of the cables may be strung linearly and axially through the girder form in straight line fashion while others of the cables may deviate from such axial alignment at various angles. For example, where a prestressed concrete I-beam having an upper head portion, a lower base portion, and a narrow interconnecting Web portion, is concerned, certain of the cables are strung through the concrete girder form so that they extend inwardly from the ends of the girder in the head portion thereof and are inclined downwardly so that they pass through the narrow web portion of the girder and enter the base portion thereof after which they extend longitudinally in straight line fashion through the base portion of the girder in the medial regions of the latter. The cables are thus caused to make a dip, so to speak, as they pass through the girder from one end to the other so that the end regions of the cables are embedded in the head portion of the girder while the medial regions thereof are embedded in the base portion of the girder. Certain other cables are caused to pass through the base portion of the girder outside the transverse confines of the web portion in straight line axial fashion. These latter cables require no hold-down anchoring devices since, when they are placed under tension by the hydraulic tensioning mechanism, they assume their straight line positions. However, those cables which are strung through the form at varying angles require hold-down devices so that when the hydraulic tensioning means is set into operation, these cables will be drawn taut in their predetermined directions of extent through the girder form. The improved 3,00ti,l l4

Patented Oct. 31, 1961 hold-down anchor device comprising the present invention is designed to facilitate proper threading of the various strands or cables which cooperate to make up the tensioning means for a prestressed concrete girder through the girder form with a minimum of effort on the part of the operator so that after the threading operation hasbeen completed, it is merely necessary to apply tension to the cables whereupon they will be drawn taut and assume their respective desired directional extent through the girder form preparatory to pouring of the concrete.

The provision of a hold-down anchor device of this type or character being among the principal objects of the present invention, it is a further object thereof to provide such a hold-down anchor which is maintained in position within the concrete girder form by conventional concrete hardware, utilizing as it does a conventional helical coil bolt socket and cooperating lag bolt such as are commonly employed in connection with coil ties, coil loops, coil rod anchors, and a wide variety of such concrete hardware.

Another object of the invention is to provide a holddown anchor device of this character which is capable of accommodating the positioning of a relatively large number of the cables so that in the installation of the cables in the concrete girder form, it is unnecessary to give detailed attention to each individual cable so as properly to position it in the form. I

A further object of the invention is to provide a holddown anchor for the tensioning cables of a prestressed concrete girder in which each of the cables accommodated thereby is given rolling tractional support by the device thus reducing frictional drag when the various cables are drawn taut or tenisoned.

A still further object of the invention is to provide a hold-down anchor device utilizing frame members which may be constructed of flat metal stock and are capable of being cut to length to accommodate the desired number of cables.

The provision of a hold-down anchor of this character which is extremely simple in its construction and which, therefore, may be manufactured at a low cost; one which is rugged and durable and which, therefore, will withstand rough usage; one which is capable of ease of assembly and which during such assembly may be built up in a progressive manner as the various cables are threaded thereinto; and one which otherwise is Well adapted to perform the services required of it, are further desirable features which have been borne in mind in the production and development of the present invention.

Numerous other objects and advantages of the invention, not at this time enumerated, will become more readily apparent as the nature of the invention is better understood.

In the accompanying two sheets of drawings forming a part of this specification, a preferred embodiment of this invention has been shown.

In these drawings:

FIG. 1 is a fragmentary longitudinal sectional view taken substantially centrally through a prestressed concrete girder of the I-beam type and having associated therewith several of the improved hold-down anchors;

FIG. 2 is a sectional view taken substantially along the line 22 of FIG. 1;

FIG. 3 is an enlarged fragmentary side elevational view of the hold-down anchor device;

FIG. 4 is a side elevational view of the structure shown in FIG. 3;

FIG. 5 is a top plan view of the structure shown in FIG. 3;

FIG. 6 is a perspective view of a spring clip employed in connection with the present invention.

FIG. 7 is a fragmentary sectional View taken subutilizing holddown anchors constructed in accordance with the principles of the present invention has been designated in its entirety at 10. The girder is in the form of an I-bearn having an enlarged lower base portion 12, an enlarged upper head portion 14 and a narrow intermediate connection web portion 16. The concrete girder 10 may have embedded therein various accessory devices, as, for example, dowel anchor inserts 18, lifting hooks 20, stirrups 22 and other functional accessories, if desired. A plurality of tensioning strands or cables 24 extend in a generally longitudinal direction completely through the girder 10 from end to end and assume various directional positions within the girder as will be described presently, these strands being firmly embedded in the surrounding mass of concrete and being initially positioned in the concrete girder form by means of a series of hold-down anchors, each of which has been designated in its entirety at 26. These anchors 26 are in the form of composite anchor assemblies, each assembly being designed to accommodate a plurality of the tensioning cables 24.

As best seen in FIG. 2, certain of the cables 24 in the longitudinal side regions of the base portion 12 extend linearly and axially through the girder in a longitudinal direction, these particular cable groups being designated at a. Another group of cables 24 designated at b extends from the upper regions of the girder at one end thereof inwardly and downwardly on an incline through the web portion 16 of the girder and into the base portion 12 thereof where they are engaged by one of the hold-down anchor devices 26 in the vicinity of a transverse plane designated at xx (see FIG. 2), after. which these strands extend horizontally along the base portion 12 and by'means of a second hold-down anchor device 26 (not shown). From the second anchor device 26, the strands in the group b extend upwardly on an incline toward the other end of the girder and pass through the web portion 16 and into the head portion 14 from whence they emerge from the girder. The groups of strands just described pass centrally through the stirrups 22 and, as best seen in FIG. 2, this group of strands is arranged in three vertical tiers which, for exemplary purposes is shown as being seven strands high. Additional groups of strands designated at arranged in two tiers on opposite sides of the group b and within the stirrups 22 similarly pass generally longitudinally through the girder and diagonally through the web portion thereof and are anchored at the lower level thereof by spaced anchor devices 26 in the vicinity of transverse planes, one of which is shown at yy, these latter planes being spaced longitudinally inwardly from the ends of the girder respectively.

The specific nature of the previously described prestressed concrete girder assembly forms no part of the present invention, except possibly insofar as the embedment therein of the various hold-down anchor devices 26 is concerned, and no claim is made herein to any novelty in connection with such a girder, the novelty of the present application residing rather in the construction of the various hold-down anchor devices 26 by means of which the cables are initially held in their proper directional orientation within the concrete girder form preparatory to pouring of the concrete, and the nature of which hold-down devices will now be more fully described and subsequently claimed.

Referring now to FIGS. 3, 4 and 5, wherein one of the hold-down anchor assemblies 26 has been illustrated in detail, each assembly involves in its general organization a generally U-shaped frame including a pair of paral- -lel side members or plates 30 of identical construction, each plate being in the form of a relatively long narrow strip of heavy gauge sheet steel. The lower end of each side plate 30 is bifurcated as at 32 (FIG. 3) to provide a pair of anchoring fingers 34 which are welded on both sides thereof as at 36 to a short length of closely wound helical coil stock 38, the various coil convolutions of which provide a series of internal threads 40 adapted to receive therein the threaded end of a lag screw 44 by means of which the anchor device may be affixed in position on the base member 46 of the concrete girder form, as will be described presently. The helical coil 38 is thus interposed between the lower notched ends of the two side plates 34) and it constitutes the sole means whereby these two plates are rigidly maintained in their fixed spaced position of parallelism. It is to be noted at this point that the adjacent ends of the side plates 30 are, by virtue of the notches therein, bifurcated to a depth greater than the axial extent of the coil 38 and that the coil is disposed wholly Within the confines of the attachment fingers 34 and is displaced axially from the upper ends of the notches in the plates. Because of the fact that the two plates 30 are of appreciable thickness, and because the notches are relatively wide, the fingers 34 are rectangular in transverse cross section and have sharp right angle inner corners which engage the coil at widely spaced regions around the generally cylindrical surface of the coil. By such an arrangement, a certain amount of flexibility is imparted to the fingers so that when welding pressure is applied thereto in directions which extend radially inwardly of the coil, the inner corners of the fingers may make good welding contact with the coil convolutions. As shown in FIGS. 3 and 4 of the drawings, the length of the attachment fingers at the lower ends of the side plates 30 is greater than the axial extent of the coil 38 and the coil is wholly disposed within the confines of the fingers and is displaced axially from the upper ends of the notches which produce the bifurcation of the lower ends of the side plates. As the result of the particular arrangement or positioning of the coil, maximum flexibility of the attachment fingers for welding purposes is obtained.

The anchor device 26 illustrated herein has, purely for purposes of illustration, been designed to accommodate the anchoring of seven tiers of vertically disposed cable strands 24, and, toward this end, the side plates are each formed with seven widened or enlarged portions 50, adjacent portions 59 being connected together by reduced neck-like portions 52. Aligned holes 54 in the opposed enlarged portions 50 are adapted to receive therethrough a plurality of traction pins 56, the various pins being in the form of conventional rivets having rivet heads 58. The pins 56 project loosely through the holes 54 and are freely rotatable therein. The distal ends of the rivetlike pins 56 are not upset in the usual manner of riveting, and thus, the pins are normally free to slide into and out of position in the holes '54 as well as to rotate freely therein, but, in order to prevent dislodgment of the assembled pins, spring clip devices 60 are employed for maintaining these pins in position.

The uppermost pin 56 in the series has its distal end threaded as at 62 for reception thereover of a nut 64, this pin and nut serving to retain the free ends of the side plates 30 against transverse spreading movement.

The various clips 60 are formed from resilient sheet metal stock and each is in the form of a generally U- shaped member (see FIG. 5) having a crown portion 63 adapted to overlie the head portion 53 of its respective, pin 56 and channel-shaped side portion 65 adapted to embrace the side edges of the enlarged portion 50 of one of the side plates 52 when the clip is in position over the head 58. The clip is installed by passing the same over the reduced neck portion 52 and sliding the same longitudinally of the side plate 30 into engagement with the adjacent enlargement 50, the crown portion 63 being guided over the rounded head 58 of the pin 56 by means of a cam finger 66 which projects laterally from the crown portion 63. Inasmuch as the uppermost threaded pin 56 has associated therewith the clamping nut 64, this latter pin does not require the use of one of the clips 60 retaining the same in position in the assembly.

In the installation and use of the present hold-down anchor device 26, holes such as have been shown at 70 in FIG. 7 are formed in the bottom or base member 46 of the concrete girder form in the regions where it is desired to install the various devices 26. The lag screws 44 are passed upwardly through the holes and are threadedly received in the helical coils 38. When the lag screws are tightened, the ends of the bifurcations 34 of the side plates 38 rest squarely on the base member 46 so that the anchor device as a whole extends vertically and is rigidly secured within the empty concrete form between the form side walls. Thereafter, the various cables associated with the hold-down devices 26 may be progressively installed in the devices. The first cable is passed between the vertically extending side plates 30 of each device with which it is associated and thereafter the lowermost pin or rivet 56 is passed through the aligned holes 54 at the bottom of each device so as to overlie the cable, so that when the cable is drawn taut by the usual hydraulic mechanism for tensioning the cables, the cable will be drawn upwardly against the lowermost pin in each assembly as clearly shown in 8 and, as tension is applied to the cable, the lowermost pin will turn in its holes 54 thus giving rolling traotional support to the cable as it seeks its position of equilibrium.

The second cable is threaded through the device in a similar manner, the pins 56 being inserted through the next adjacent series of opposed holes 54 above the cable and the operation is continued until the last cable is threaded between the side plates 30. The final step in the assembly is the insertion of the threaded pin or rivet 56 through the uppermost series of aligned holes 54 and the application thereto of the clamping nut 64, this nut, in combination with the head 58 of the pin, serving to retain the two side plates '39 against spreading movement, as previously described.

When all of the cables have thus been threaded through the various hold-down anchor devices according to the cable pattern illustrated in FIGS. 1 and 2, or according to any other desired cable pattern, the ends of the cables are attached in the usual manner to the hydraulic tensioning mechanism and when tension is applied to these cables, the cables will assume the positions wherein they are shown in FIGS. 1 and 7 preparatory to pouring of concrete.

After the concrete has been poured and allowed to become set, the lag screws 44 may be unthreaded from the various coil anchors 38 and withdrawn from the form assembly after which the assembly may be knocked down, and the projecting or protruding ends of the various cable strands 24 severed flush with the ends of the girder to complete the article.

The invention is not to be limited to the exact arrangement of parts shown in the accompanying drawings or described in this specification, as various changes in the details of construction may be resorted to without departing from the spirit of the invention. Only insofar as the invention has particularly been pointed out in the accompanying claims is the same to be limited.

This application is a continuation of United States patent application Serial No. 681,360, filed by me on August 30, 1957, and entitled Hold Down Anchor Device for the Embedded Cables or Prestressed Concrete Girders, now abandoned.

Having thus described the invention what I claim as new and desire to secure by Letters Patent is:

1. A hold-down anchor device for positioning the tensioning cables of a prestressed concrete girder within a girder form preparatory to concrete pouring operations, said anchor device comprising, in combination, a generally U-shaped, normally upstanding frame including a pair of flat spaced parallel side plates having appreciable thickness, and a connecting base extending between the lower ends of said side plates, said base being formed with an internally threaded bore adapted to receive therein the threaded end of a lag bolt whereby the frame may be secured to the base support of the girder form with the side plates extending vertically upwardly from said base support within the confines of the form, said base being in the form of a closely wound helical coil of rod stock, said side plates having the lower ends thereof provided with longitudinally extending notches which extend upwardly from the bottom edges of the side plates and serve to bifurcate said lower ends of the side plates and form attachment fingers of rectangular cross section and with sharp right angle inner corners, each of said fingers having its sharp right angle inner corner welded to the outer surface of the coil along an axial line of tangency, said side plates being provided with a series of opposed pairs of holes therein with the various pairs being spaced progressively along the side plates outwardly from said base, and a traction pin received in each pair of opposed holes, each pin being adapted to overlie and tractionally engage one of hte tensioning cables so as to receive the upward thrust thereof and space the same from said base support at the point of contact therewith when the cable is drawn taut.

2. A hold-down anchor device for positioning the tensioning cables of a preseressed concrete girder Within the girder form preparatory to concrete pouring operations, said anchor device comprising, in combination, a generally U-shaped frame including a pair of spaced parallel side plates and a connecting base extending between one pair of adjacent ends of said side plates, said base being formed with an internally threaded bore adapted to receive therein the threaded end of a lag bolt whereby the frame may be secured to the base support of the girder form with the side plates extending vertically upwardly from said base support within the confines of the form, said side plates being provided with a series of opposed pairs of holes therein with the various pairs being spaced progressively along the side plates outwardly from said base, a traction pin removably received in each pair of opposed holes and freely rotatable therein, each pin having a cylindrical shank portion projecting completely through said opposed holes and an enlarged head for preventing withdrawal of the pin from said opposed holes in one direction, each pin being adapted to overlie and tractionally engage one of the tensioning cables so as to receive the upward thrust thereof and space the same from said base support at the point of contact with the pin when the cable is drawn taut, and a U-shaped retaining member for each traction pin having side portions embracing the side edges of one of said plates and a crown portion overlying the head of said pin and serving to prevent withdrawal of the pin from said opposed holes in the opposite direction.

3. A hold-down anchor device as set forth in claim 2 and including, additionally, an additional traction pin having an enlarged head and a shank portion received in one of said pairs of opposed holes in the side plates, said latter shank portion being threaded, and a nut threadedly received on said threaded shank and serving with said head to prevent withdrawal of said latter pin from said opposed holes.

4. A hold-down anchor device as set forth in claim 3 and wherein said additional traction pin has its shank portion projecting through the outermost pair of opposed holes in the series.

5. A hold-down anchor device for positioning the tensioning cables of a prestressed concrete girder within the girder-form preparatory to concrete pouring operations, said anchor device comprising, in combination, a generally U-shaped frame including a pair of elongated spaced parallel side plates, and an interconnecting base support extending between said side plates and adapted to be secured to the base support of the girder form within the confines of the form with said side plates extending upwardly from said base support, said side plates being provided with a series of longitudinally spaced relatively wide portions with adjacent wide portions being connected to each other by a relatively narrow reduced neck portion, said wide portions of the side plates respectively being transversely opposed, each pair of opposed wide portions being formed with aligned holes therethrough, a traction pin removably received in each pair of opposed holes and freely rotatable therein, each pin being adapted to overlie and tractionally engage and re? ceive the upward thrust of one of the tensioning cables so as to space the same from said form base support at the point of contact therewith when the cable is drawn taut, each of said pins being formed with an enlarged head for preventing removal of the pin from its respective holes in one lateral direction, and a retaining clip for each pin preventing removal of the pin from its respective holes in the opposite direction, said retaining clip having opposed guideways embracing the lateral sides of one of said wide portions of one of the side plates, and a crown portion overlying the head of one of said traction pins, said guideways being spaced apart a distance greater than the width of said neck portions whereby the clip may be moved into register with the adjacent neck portion and removed from the side plate.

6. A hold-down anchor device as set forth in claim 1 and wherein the length of the attachment fingers is greater than the axial extent of the coil and the coil is wholly disposed within the confines of the fingers and is dis placed axially from the upper ends of the notches.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Richmond Catalogue, 1943, by Richmond Screw Anchor Co. Inc, Brooklyn, N.Y., p. 15, item F, H-Flange Hanger. 

